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Fundamentals: Waste Water Heat Recovery

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    • CommentAuthorEd Davies
    • CommentTimeJun 24th 2013
     
    Sorry, bit of thread drift but do plate heat exchangers in combi boilers have an air gap?
    • CommentAuthorDarylP
    • CommentTimeJun 24th 2013
     
    ... no:bigsmile:
    • CommentAuthorbarney
    • CommentTimeJun 24th 2013
     
    and how could they, with any efficiency or quite complicated manufacturing ?

    Heating system fluid is usually far more contaminated than shower water - at least a Category 3 fluid - and no one worries about that when the filling loop is left connected and system pressure exceed MCWS pressure

    Regards

    Barney
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 24th 2013
     
    Spa Baths are vile places, worse job I ever had to do was cleaning out the DE filter at the Sheffield YMCA. I have do idea what those young men got up to :shamed:
    •  
      CommentAuthordjh
    • CommentTimeJun 24th 2013
     
    Posted By: SteamyTeaBut with electricity at 0.18p/kWh it is a saving of £67/annum making the payback 7.5 years if the unit is £500.

    I hope that nobody on here believes that using mains electricity resistance heating is a way to justify one of these devices? Get a more efficient water heater instead.
    Becomes marginal there, but as you rightly say, reduce the usage only saves you money.

    I think that's backwards. Reducing usage saves water, energy and money. These devices may or may not save money and energy but definitely don't save water.
    • CommentAuthorSeret
    • CommentTimeJun 25th 2013
     
    Posted By: barneyA shower in a domestic dwelling is generally a Category 3 fluid - a simple backflow device like a double check valve would satisfy WRAS requirements.

    Regards

    Barney


    Thanks Barney. That's so easy I'll stick one in pronto.

    I fitted my unit yesterday. Seems to be doing something, in the shower I took yesterday I was able to turn the shower down quite a bit from the usual setting to get the same temperature. I haven't got the shower instrumented, so I'll have to wait for a few weeks gas readings to see if there's a noticeable impact on usage.
    • CommentAuthorRobL
    • CommentTimeJun 25th 2013
     
    This is a pretty innovative product - it's in Oz though, and I can't see a WRAS cert :-(
    In a nutshell, shower water is centrifuged to clean it a bit, it's UHT heated, and mixed with a third extra fresh water before going to the shower head. They claim to re-use 70% less heat & water, for the actual same shower experience.

    http://www.recyclingshower.com.au/
  8.  
    I'm planning some hot water heat recovery for my build project.
    I've got more than one shower, a bath, a washing machine, so after seeing quite a few commercial options I'm going for the "heat squirrel". It's a 120 litre holding tank for any "waste" hot water. Incoming cold water to your heating system / hot water tank, goes through pipes inside this "heat squirrel' tank, so it should pick up some of the heat from the hot water. It also means 120 litres of water is held inside your house before it heads away.

    Some information on what I've found on this topic, and the heat squirrel is at http://www.silverspray.co.uk/2012/03/26/ecobuild-waste-water-drain-water-shower-heat-recovery/

    By holding the hot water, there is more time for the heat transfer to any incoming cold water, especially any that sits in the coil inside the heat squirrel.
    Hopefully this 120 litres of water is regularly self flushing as “grey water very quickly turns manky when stored, even for short periods.”
    • CommentAuthorEd Davies
    • CommentTimeJun 27th 2013
     
    System doing heat recovery just for space heating and water re-use:

    http://www.theyellowhouse.org.uk/themes/heatwat.html#h14
    • CommentAuthorSilverSpray
    • CommentTimeJun 28th 2013 edited
     
    Posted By: SeretAny further info on that Heat Squirrel? I've contacted the company, but just wondering if you had done any research.

    Was planning on building a heat recovery tank into my extension plans, had intended to build my own but I must admit a premade one does appeal to my lazy side.


    Seret,
    I've spoken to them and another company who has installed a heat squirrel. The company that installed it for a client of theirs said they had a happy client. There doesn't seem to be much more info, but I don't know what extra info you'd want ?
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 28th 2013 edited
     
    Was at the Green Cornwall Show chatting to a thermodynamic panel fitter, they seemed to think they worked well but was a bit shady about the reliability, just claiming that they do tto know of any problems.
    • CommentAuthorSilverSpray
    • CommentTimeJun 29th 2013 edited
     
    SteamyTea: Who was the Thermodynamic panel fitter ?

    Seret: I don't think the Heat Squirrel has any controls. It works by virtue of the inbound cold mains water flows through the tank of 120 litres of your waste hot water. By there being a long coil route through the Heat Squirrel tank there is a long surface area and time (both matter) to transfer heat to the cold mains water.
    I've added the schematic and installed Heat Squirrel images I had to the page.
    See http://www.silverspray.co.uk/2012/03/26/ecobuild-waste-water-drain-water-shower-heat-recovery/#heat-squirrel
  13.  
    On the Heat Squirrel. I found some of my other notes.

    - They are about £399 (not installed). The heat squirrel has a 120 litre capacity.
    - Can the waste water input be regulated so that only waste water that is warmer than the water in the heat squirrel is let in to it? I don't see why a temp sensing valve can't do this.
    - It seems that for a shower, the recoupenergy solutions will be the most efficient, but for the whole house, and the total cost, a single heat squirrel could be best.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJun 29th 2013
     
    Posted By: SilverSprayWho was the Thermodynamic panel fitter ?

    www.greenairsouthwest.co.uk

    They have a nice oil price chart, shows that it is currently $102.10/barrel and going down. Iam sure a bit of code could be written to only show it when it is going up.
    • CommentAuthorSeret
    • CommentTimeJun 29th 2013
     
    Posted By: SilverSpray
    - Can the waste water input be regulated so that only waste water that is warmer than the water in the heat squirrel is let in to it? I don't see why a temp sensing valve can't do this.


    This seems crucial to me, but it doesn't look like any such thing is fitted. That schematic does show a "temp sensor pocket", but it's not clear if that's for anything in particular. I'm also a bit sceptical of the way they show something like a washing machine or a dishwasher feeding it. Unless you have your dishwasher upstairs I can't see that working.
    •  
      CommentAuthordjh
    • CommentTimeJun 29th 2013
     
    Posted By: SilverSprayCan the waste water input be regulated so that only waste water that is warmer than the water in the heat squirrel is let in to it? I don't see why a temp sensing valve can't do this.

    I would guess valves are designed for clean water, not for water with various kinds of goop in it. It's bad enough cleaning out a trap, how would you clean a thermostatic valve?
    • CommentAuthorwholaa
    • CommentTimeDec 25th 2019
     
    Has anyone tried the Showersave QB1-21? Based on what I read on these forums I had a negative perception of these systems but I saw it mentioned in PassiveHouse plus.

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